The present invention relates generally to diagnostic imaging and, more particularly, to a method and apparatus of dynamically filtering radiation emitted toward a subject during radiographic imaging.
Typically, in radiographic imaging systems, an x-ray source emits x-rays toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” may be interchangeably used to describe anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-rays. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
In computed tomography (CT) imaging systems, the x-ray source and the detector array are rotated about a gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-rays as a beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and a photodiode for receiving the light energy from an adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
There is increasingly a need to reduce radiation dosage projected toward a patient during an imaging session. It is generally well known that significant dose reduction may be achieved by using a “bowtie” filter to shape the intensity profile of an x-ray beam. Surface dose reductions may be as much as 50% using a bowtie filter. It is also generally known that different anatomical regions of a patient may advantageously mandate different shaped bowtie filters to reduce radiation dosage. For example, scanning of the head or small region of a patient may require a bowtie filter shaped differently than a filter used during a large body scanning session. It is therefore desirable to have an imaging system with a large number of bowtie filter shapes available to best fit each patient. However, fashioning an imaging system with a sufficient number of bowtie filters to accommodate the idiosyncrasies encountered during scanning of numerous patients can be problematic in that each individual patient cannot be contemplated. Additionally, manufacturing an imaging system with a multitude of bowtie filters increases the overall manufacturing cost of the imaging system.
Therefore, it would be desirable to design an apparatus and method of dynamically filtering the radiation emitted toward the subject during imaging data acquisition with a single filter.